Under the volcano: this is what happens before the eruption

The Mauna-Loa in Hawaii, the Semeru on the island of Java and the Stromboli in the Aeolian Islands. Three large volcanoes have fired 2022 shaking the earth.

In May 2022 Etna was the protagonist and in September 2021 it coincided in eruption with the Tajogaite volcano on the island of La Palma. Now one year has passed since the end of this eruption and it might seem that a page has been closed. But the Earth is still alive and great volcanic eruptions are always probable, both the spectacle they represent and the tragedies they bring with them.

El Tajogaite caused the evacuation of more than 7,000 people, many of whom lost their homes and even their livelihoods, the destruction of roads and basic infrastructure, and the formation of lava flows that devastated more than 1,200 hectares with thicknesses that in some places reached 70 m. Without forgetting other consequences that are now appearing, such as continuous gas emissions, respiratory problems, skin pathologies, mental and anxiety problems in the population that will take a few years to fix. Thus, research to detect precursors of these volcanic eruptions is, if possible, even more important.

under the volcano

To anticipate the eruption, we must understand what happens under a volcano before it occurs. The heat and pressure are so high inside the mantle that it causes rocks and gases to melt, forming magma. These high pressures and temperatures make the magma try to escape through the earth’s crust, looking for fractures or weak areas to progress in its ascent. When it finds one of these structurally weaker zones, it accumulates in them, forming reservoirs that we call magmatic chambers.

The rise of the magma can be very fast or so slow as to invest up to decades in it. On this trip, successive magmatic chambers are formed. When there are a few kilometers left to reach the exterior, signs appear on the surface in the form of gases that emanate, earthquakes produced by the rupture of the crust in the ascent of the magma and deformations of the terrain. The latter caused by the positive pressure of the magma and the horizontal and vertical breaks of the crust.

Detect magma before it reaches the surface

During the course of the volcanic eruption of La Palma in 2021, researchers from the Institute of Geosciences (IGEO-CSIC), together with other researchers from the Complutense University, the Polytechnic University of Madrid and researchers from different foreign centers in Italy, Canada and the United States Together we began to work on a technique that has managed to detect the accumulation of magma in an area close to the surface, months before the eruption occurs.

This technique is based on the study of those ground deformations produced by the rise of magma before the eruption and the breaks in the crust, recorded by latest generation satellite radar interferometry (InSAR) observation techniques, combined with a new technique for interpreting these deformations.

Precursor signs of the eruption

The eruption of the Tajogaite volcano on La Palma began on September 19, 2021 on the western slope of Cumbre Vieja and was active for 85 days, generating lava flows that are added to those from previous eruptions on this slope.

Our results show that about three and a half months before the eruption a rise of magma appears, which grows over time, thus forming a magma reservoir at a depth of about 2.5 km in a structurally weak, fractured and porous zone.

In the image that follows this paragraph, we have represented in red the strong positive pressure under the earth’s surface probably caused by the intrusion of magma. This is suggested by this path of points, which would occur under the town of Jedey, being about 5 km south of the main volcanic cone of the eruption. Two months before the eruption, vertical fracturing sources (represented in yellow) begin to appear at a depth of about three thousand meters, suggesting a brittle crustal response due to stronger magma ascent.

Coinciding with the seismic activity prior to the eruption, the appearance of these sources of fracturing and tension increases, which we associate with the magma dam that used that fissure to come to the surface. In these pressure and tension structures, in addition to the main branch associated with the eruption, two other ascending branches are activated, also represented in red in the image below. These two branches are located one under the ocean to the south of Puerto Naos and the other to the west of the town of jedeywithout reaching the surface as failed magma intrusions.

The model of magmatic reservoir, magma rise and associated terrain fractures obtained in this study would also help to explain other phenomena, such as the still continuous emission of gases in the areas of Puerto Naos and La Bombilla.

Are we closer to being able to anticipate volcanic eruptions?

The results of this methodology, which have been published in the journal Scientific Reports, show that this technique can help in the detection and monitoring of new episodes of volcanic reactivation. Also to determine the potential areas of magma accumulation, help in the determination of the possible paths of eruption and advance in the forecast of the start of a next eruption in La Palma, the Canary Islands, as well as in other active volcanic islands.

Are we now closer to being able to anticipate volcanic eruptions? We cannot answer it with a resounding yes, unfortunately there is still a lot of research to be developed in this field. The results that have been obtained in the study of this eruptive process do seem to help to move in this direction, it would even be very useful in the design and planning of infrastructures and urban development in the reconstruction of the island after the eruption. We can know a lot about what happens under the volcano, and this can allow us to anticipate the catastrophe. (YO)